import java.util.Scanner;

//TIP 要<b>运行</b>代码，请按 <shortcut actionId="Run"/> 或
// 点击装订区域中的 <icon src="AllIcons.Actions.Execute"/> 图标。
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        scanner.close();

        int hits = 0;
        int consecutiveHits = 0;

        while (n > 0) {
            hits++;
            consecutiveHits++;
            n -= 2;

            if (consecutiveHits == 3) {
                n -= 10;
                consecutiveHits = 0;
            }
        }

        System.out.println(hits);
    }
}